U.S. patent application number 14/430225 was filed with the patent office on 2015-09-03 for portable medical device system.
The applicant listed for this patent is 12R MEDICAL LIMITED. Invention is credited to Ian Hardman, Keith Heaton.
Application Number | 20150246164 14/430225 |
Document ID | / |
Family ID | 47190423 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150246164 |
Kind Code |
A1 |
Heaton; Keith ; et
al. |
September 3, 2015 |
Portable Medical Device System
Abstract
The present invention provides an apparatus comprising a wound
dressing (15) connected to a fluid container (11) via a pump (3),
wherein the wound dressing is in communication with a mechanical
pressure control valve (13), the fluid container is provided with
an inlet (2) and an outlet (4). Also provided are (i) flexible
fluid containers comprising of at least two layers of film with an
integrated vent, (ii) wound dressings and (iii) a multi-compartment
wound fluid container (20, 35, 63) comprising at least two internal
compartments and provided with an outlet (31, 37, 51) and an inlet
(19, 49), in which the container comprises a microporous fluid
separator (29, 41, 55) which divides the at least two internal
compartments, wherein the microporous fluid separator permits gas
flow between the compartments and prevents fluid flow to the outlet
of the container. Other apparatus provided comprises a means for
detecting the level of fluid within a multi-compartment wound fluid
container as described. The invention also provides a system for
applying a sub-atmospheric pressure to a wound dressing on a
patient using devices and apparatus of the invention and methods of
treatment of wounds using such apparatus, devices and systems of
the invention.
Inventors: |
Heaton; Keith; (Dorset,
GB) ; Hardman; Ian; (Dorset, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
12R MEDICAL LIMITED |
Dorset |
|
GB |
|
|
Family ID: |
47190423 |
Appl. No.: |
14/430225 |
Filed: |
September 20, 2013 |
PCT Filed: |
September 20, 2013 |
PCT NO: |
PCT/GB2013/052465 |
371 Date: |
March 22, 2015 |
Current U.S.
Class: |
604/313 |
Current CPC
Class: |
A61M 2209/088 20130101;
A61M 1/0031 20130101; A61M 1/0096 20140204; A61M 1/0088 20130101;
A61M 2205/8206 20130101; A61M 1/0092 20140204; A61M 2205/3331
20130101 |
International
Class: |
A61M 1/00 20060101
A61M001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2012 |
GB |
1216928.0 |
Claims
1-30. (canceled)
31. An apparatus comprising a wound dressing connected to a
flexible fluid container via a peristaltic pump, wherein the wound
dressing is in communication with a mechanical pressure control
valve, and the fluid container is provided with an inlet and an
outlet, in which the pressure control valve is connected to the
wound dressing via a tubing connector.
32. An apparatus as claimed in claim 31, in which the fluid
container outlet is a gas vent.
33. An apparatus as claimed in claim 31, in which the fluid
container outlet is a valve.
34. An apparatus as claimed in claim 31, in which the flexible
fluid container comprises at least two layers of a polymeric film
and a vent which comprises a hydrophobic membrane.
35. An apparatus as claimed in claim 31 comprising a means for
detecting the level of fluid within the flexible fluid container,
in which the container is constrained by a flexible strap.
36. An apparatus as claimed in claim 35 in which the means of
detecting the level of fluid within a wound fluid container is by
operation of a pressure sensitive switch.
37. An apparatus as claimed in claim 36 in which the pressure
sensitive switch is a micro-switch.
38. An apparatus as claimed in claim 35 in which the correct
position of the flexible strap is detected by a proximity
switch.
39. A system for applying a sub-atmospheric pressure to a wound
dressing on a patient, wherein the system comprises an apparatus as
claimed in claim 1 and a control means.
Description
[0001] The present invention relates to apparatus for Negative
Pressure Wound Therapy (NPWT) in patients suffering from exposed
wounds.
[0002] Negative Pressure Wound Therapy, Reduced Pressure Therapy or
Sub-Atmospheric Pressure Therapy is used to treat hard to heal
wounds and works on the principle of applying a sub-atmospheric
pressure (normally between 50 mmHg and 200 mmHg gauge pressure) to
a porous dressing situated at the wound site. Typically the porous
dressing would be held in place with a partially occlusive adhesive
film and a tube connects the dressing assembly to a rigid fluid
container fitted to the pressure generating device, which consists
of a low flow vacuum pump, a receptacle for the fluid container, a
control system and a moulding to house the various components. In a
typical device in clinical use a control system energises the pump
which in turn evacuates the dressing and draws air and fluid out of
the wound dressing site via the tube into the rigid container. When
the air has been evacuated a negative pressure is established at
the wound site which is communicated back to the container inside
the pump unit housing via the tubing, this in turn is communicated
to the control system within the unit housing. The control system
regulates the vacuum pump to maintain the required set pressure.
Examples of NPWT systems in clinical use are the InfoVAC.RTM.
manufactured by KCl of San Antonio, Tex., USA and Renasys.RTM.
system manufactured by Smith and Nephew of Hull, UK.
[0003] Conventional means of collecting wound fluid in a Negative
Pressure Wound therapy system comprises of a vacuum port and a
fluid inlet port incorporated into a rigid sealed plastic
container. A negative pressure is generated within the rigid
container by evacuating the air within the container via the vacuum
port where fluid is then drawn into the container. A hydrophobic
filter prevents fluid being drawn into the vacuum port, see for
example WO 2000/061206. A limitation of this technique is that the
container has to be sufficiently rigid to withstand the negative
pressure generated within the container, typically up to 300 mmHg.
Additionally the container occupies a fixed volume in both the
unfilled and filled condition which could be up to 1000 cm.sup.3.
This has implications for material cost, storage and potentially
prevents the use of the therapy in a portable application due to
size and patient comfort. In addition to controlling pressure by
varying the pump speed one method is to provide a proportional
valve mechanism between the inlet and outlet ports of the vacuum
source. This valve can move between the open and a closed position
and between the vacuum source and the wound fluid container to
regulate the pressure at the wound site. The valve mechanism is
controlled by a control unit that receives pressure signals from a
transducer. An example of this approach is described in US
2010/0204663. The disadvantage of this technique is that it
requires electronic circuitry to measure and provide signals to
control a proportional valve. Furthermore, by controlling pressure
within the vacuum source housing there are inevitable pressure
drops and hydrostatic head effects that can alter the accuracy of
the pressure delivered at the wound site.
[0004] In addition to a standard diaphragm air vacuum, a
peristaltic pump or other type of peristaltic pump can be used to
generate a negative pressure. The advantage of using a peristaltic
pump to remove fluid is that the fluid can be contained within the
tube and a suitable container.
[0005] A pressure sensor can be provided at the wound site and a
signal sent back to the unit controlling the pump via an electrical
wire in the fluid tubing. Depending on the signal from the pressure
sensor then the drive voltage to the pump can be altered. The use
of a peristaltic pump for applying a vacuum pressure to a wound is
described in includes US 2007/0055209. The disadvantage of using a
peristaltic pump in this way is the inability to provide effective
pressure control at the wound site, reducing the speed of the pump
does not effectively reduce the pressure at the wound site because
of the sealed nature of the peristaltic pump system. Without any
opening to the atmosphere, the pressure at the wound can be
maintained for a long period of time even when the pump is switched
off because it is a sealed system. Additionally providing an
electronic sensor at the wound site provides additional
complications and potential safety concerns especially in a
portable system for the home.
[0006] An alternative means of collecting fluid in an expandable
container consists of utilising a wicking element that is attached
to a body incorporating the inlet and outlet connections. Fluid is
drawn into the body via the fluid port and a wicking component
transfers the fluid into the expandable portion of the container,
see for example WO2009/106895.
[0007] Negative Pressure Wound Therapy (NPWT) was first introduced
into clinical practice over 15 years ago. Since then the body of
evidence for its use in both the hospital and community setting has
grown rapidly. The technology was originally developed for the
treatment of complex wounds within the hospital environment. Recent
studies have identified that the use of NPWT in the community can
offer significant advantages from both an economic and patient
benefit perspective. The economic and social benefits are derived
from the possibility to deliver an effective therapy into the
community at an economic price to the healthcare provider. If a
patient is discharged early with a complex wound and it starts to
regress in the community the cost can quickly escalate with the
additional nursing costs involved and potential readmission. Costs
increase dramatically if the wound becomes infected and high
dependency or intensive care treatment is involved.
[0008] In addition to the economic cost there is a large human cost
associated with living with complex wounds. However traditional
NPWT systems are not ideally suited for use in the home due to the
size of the unit required to house the vacuum pump, control system
and the receptacle required for the fluid container. Additionally
hospital style NPWT systems also require the disposal of the
components that are in direct contact with the wound fluid. This
typically includes the dressing components, PVC tubing and the
fluid container systems which can range in size from 300 ml to 1000
ml.
[0009] Some portable systems have been developed for use in the
community such as the Pico.TM. system manufactured by Smith &
Nephew which consists of a dressing system and a small pump system
and where the entire system is disposed after a course of
treatment. Typically portable systems either consist of a
traditional style rigid fluid container with a smaller capacity to
ensure the overall system size is reduced or a passive
super-absorbent dressing that absorbs the wound exudate.
[0010] Monitoring and control of pressure at the wound site is
achieved in several different ways by commercial devices currently
on the market. KCl (San Antonio, Tex.) utilises a technology called
T.R.A.C.TM.. This consists of a multi-lumen tube consisting of a
fluid path and sensing lumens which transmit the pressure at the
wound site to a pressure sensing circuit in the product
housing.
[0011] Other commercial devices utilise a system that measures
pressure inside the fluid container on the wound side of the
protective hydrophobic filter. The pressure feedback control
electronics then regulates the pump power to meet the target
pressure.
[0012] Other commercial systems provide a fixed bleed within the
pneumatic system to stimulate flow and aid pressure control
[0013] With regard to the problem associated with orientation of
the canister or movement causing the filter to occlude before the
container is full, solutions have been tried that include the
addition of a super absorbent gel within the container that
partially solidifies the fluid to prevent wetting of the filter.
Other designs have been tried that involve compartmentalising of
the rigid canister structure that provides multi-facets of the
filter in different planes.
[0014] Most commercial devices utilise a diaphragm pump that
normally consists of a brushed or brushless DC motor that is
controlled by an electronic controller consisting of pressure
transducers and motor drive circuitry. Typically these pumps can
generate up to 350 mmHg vacuum pressure and generate a flow of
between 2 to 10 litres per minute.
[0015] The wound fluid is typically collected in a rigid moulded
container that is made from a suitable injected mouldable grade
polymer such as a clear ABS that may also be a grade capable of
withstanding Gamma radiation. Within the canister a hydrophobic
filter is welded or bonded in place. The individual plastic
components are ultrasonically or chemically bonded together to
provide an hermetic seal where typically a length of PVC tube (1 to
2 metres) is bonded into the container assembly. In some cases the
entire assembly is sterilised by Gamma irradiation or Ethylene
oxide (EtO) gas and then packaged. This assembly is disposed of as
clinical waste once the container has reached its capacity.
[0016] Increasingly complex wounds are being treated in the home
due to the ageing population and pressures on hospitals to
discharge patients earlier. These complex wounds often produce
significant levels of wound exudate that are beyond the capacity of
an absorbent dressing and require an effective means of removing
the fluid from the wound site in conjunction with the delivery of a
consistent level of pressure at the wound site. Traditional methods
of containing wound fluids in a NPWT device consists of a rigid
plastic moulding manufactured from a thermoplastic material such as
Acrylonitrile butadiene styrene (ABS) and incorporating a
hydrophobic filter to contain fluid within the container. Typically
these containers hold between 300 ml and 1000 ml and are
rectangular in shape and fit into a customised receptacle within
the pump system enclosure.
[0017] The containers are rigid to withstand the vacuum pressure
generated within them which can potentially be up to 350 mmHg in a
fault condition and is normally up to 200 mmHg in normal
conditions. Conventional flexible bags such as those used in urine
or colostomy collection applications have previously not been able
to be utilised because they collapse when subject to the negative
pressure thus preventing fluid being removed from the wound site
and pressure being applied to the wound site.
[0018] Typically the vacuum port is at the top of the canister and
is protected by a hydrophobic filter. Depending on the type of
system used typically detection of a full container is achieved by
a non-contact electronic device such as a capacitive sensor. Other
methods include allowing the canister to fill with fluids until the
hydrophobic filter is occluded; this results in the pressure
between the pump and the filter to increase while the pressure in
the container or the wound dressing decays. The system software
detects the pressure differential and interpolates this as an
indication of a full container.
[0019] One problem with these methods are that they are prone to
premature detection of a full container if the unit and the
container are tilted or shaken such as can occur through walking or
ordinary movement of a patient. Additionally if the unit is placed
on its side or upside down it will trigger the alarm even if there
is minimal fluid in the container resulting in the patient or user
having to replace the container. In view of the sealed nature of
the container it cannot be emptied and needs to be disposed of even
if it is only partially filled, this has an economic effect and
also an environmental impact.
[0020] These issues are not prevalent when the product is used in
the static hospital situation but can become a major problem when a
patient is discharged from hospital with a complex wound back into
the community. In order to promote wound healing patients are
encouraged to be ambulatory but hospital style NPWT devices do not
support this because of the size and weight of the products due in
part to container size and control systems and also the need to
keep the fluid container in an upright static position.
[0021] Another problem present with the use of NPWT in the home
concerns the pressure control system. To ensure effective therapy
is delivered a relatively constant negative pressure at the wound
site needs to be maintained. If the pressure at the wound site is
not accurately controlled then this can lead to a series of
problems including inconsistent wound healing, pain and in extreme
cases bleeding. As well as accurate pressure control there is also
a need to maintain a minimum level of flow from the wound site.
Potentially with a sealed dressing a situation can exist where is
there is little or no flow from the wound site to the wound fluid
container.
[0022] This can lead to the wound exudate "pooling" at the wound
site which can lead to a series of problems including breakdown of
the seal of the covering film to the skin, maceration of the
periwound skin area and potentially an increase in infection at the
wound site. Maintaining consistent pressure and flow at the wound
site becomes increasingly important with patients who have been
discharged from hospital with complex wounds. However increased
mobility leads to additional difficulties in controlling pressure
and flow rates at the wound site which does not always occur in
hospital situations when the patients are lying down and relatively
immobile. One particular issue is the potential height difference
that can exist between the pump and the wound site, which is often
the case when a leg or foot ulcer is being treated. This can result
in a pressure difference of up to 75 mmHg depending on the length
of tubing used which is due to the hydrostatic pressure present on
the wound fluid. If the system is controlling pressure within the
pump control unit this can result in a reduced pressure at the
wound resulting in reduced therapeutic effectiveness and
compromised wound fluid drainage. Similarly moving the pump unit
below the wound can in some cases result in a spike of
pressure.
[0023] Pressure control in traditional NPWT devices is achieved by
the use of pressure transducers measuring pressure within the pump
unit and comparing it with the desired pressure. The pump pressure
is then adjusted via the electronic control system to match the
actual pressure at the measurement point to the desired set
pressure. Problems with this arrangement include the discrepancy
between the pressure measured at the pump unit and the actual
pressure at the wound site. This discrepancy can be caused by the
pressure drop across the protective hydrophobic filter or a height
difference between the pump unit and the dressing as described
above or the viscosity of the wound fluid. The pressure discrepancy
between the pump unit and the dressing can be compensated by having
a second pressure transducer sensing pressure at the wound side of
the filter or at the wound dressing itself. However this requires
complex arrangements of tubing separating the air path from the
fluid path, a second pressure transducer, a safety release solenoid
and electronics to receive and condition the signal from the
transducers and a software algorithm to convert this into an output
signal that will drive the pump at the correct level to achieve the
target pressure.
[0024] In summary user problems that require solving include:
[0025] Providing a means of delivering effective NPWT therapy in
the home (wound fluid removal and accurate pressure control).
[0026] Allowing NPWT to be administered to ambulatory patients.
[0027] Remove the requirement for a rigid container thus reducing
size and environmental impact. [0028] Providing a means of
collecting the fluid so it can be easily disposed of in the home
environment whilst reducing the risk of contamination and cross
infection. [0029] Transmission of fluid from the wound site to the
dressing is critical, without this the fluids can collect at the
wound increasing the risk of infection through an increase in
Colony Forming Units (CFU's) and potentially cause maceration of
the peri-wound area. [0030] The fluid container needs to function
in multi-orientations. [0031] The product should be discrete (small
and quiet).
[0032] Technical issues associated with these are: [0033] Providing
accurate pressure control at the wound without the need for
multiple tubes and sensors to the wound site and the associated
level of complexity in the electronic control system and software.
[0034] Providing a means to allow fluid to be drawn away from the
wound at a constant flow preventing the fluid "pooling" at the
wound site. [0035] Allowing air flow to be applied at the wound
site whilst fluid is removed into a fluid container and still allow
the product to operate in multi-orientations. [0036] Ensure the
wound fluid is separated from external contact or potentially
reusable components. [0037] Provide a means of collecting fluid in
a flexible container whilst subjecting the container to negative
pressure. [0038] Enable gas flow through the canister in any
orientation. [0039] Ensure any filtration means when challenged by
the fluid (which occurs more often in mobile situations) provides a
high level of bacterial retention whilst still able to support a
flow rate of fluid away from the wound. [0040] Power levels need to
be very low to support the use of small batteries. [0041] The
source of negative pressure should be virtually silent.
[0042] According to a first aspect of the invention there is
provided an apparatus comprising a wound dressing (15) connected to
a fluid container (11) via a pump (3), wherein the wound dressing
is in communication with a mechanical pressure control valve (13),
the fluid container is provided with an inlet (2) and an outlet
(4).
[0043] The wound dressing may be a negative pressure wound therapy
dressing. The dressing may comprise an absorbent pad (for example a
porous pad) and/or a flexible layer (for example a film layer). The
absorbent pad in the wound dressing may be composed of any suitable
material, such as for example a polyurethane reticulated open cell
foam and/or gauze (e.g. cotton, polyester/cotton blend, etc.). The
flexible layer may be any suitable film, for example a polymeric
film for use in wound dressings, in particular a negative pressure
wound therapy dressing, such as for example a hydrophobic polymeric
film.
[0044] Suitably, the pressure control valve is connected to the
wound dressing via a tubing connector. The connector may be adhered
to the dressing and may suitably be of separate construction. The
connector may include the vacuum tube and the pressure control
valve. Alternatively, the connector may attach the pressure control
valve to the tubing between the dressing and the fluid container or
vacuum source. In some embodiments of the invention, the outlet can
vent pressure in the container to the external atmosphere.
[0045] According to the present invention, the wound dressing is
connected to the fluid container so as to allow air and fluid to
pass from the wound dressing into the fluid container through the
action of the pump which causes a negative air pressure to be
exerted at the side of application of the wound dressing. The wound
dressing is therefore in gaseous communication with the fluid
container.
[0046] The mechanical (non-electrical) pressure control valve may
also be present as part of the wound dressing, integrated or
embedded within the dressing components e.g. the film, tubing
connector or dressing foam or pad. The wound dressing may be
suitably connected via tubing to the fluid container. The tubing
may be composed of any suitable polymeric material, such as for
example polyurethane, PVC or silicone. The tubing may be vacuum
tubing or other suitable tubing able to withstand a negative
pressure. Alternatively, the wound dressing may be directly
connected to the pump and/or the pump connected directly to the
fluid container.
[0047] The fluid container (11) can be rigid or flexible and can be
of any suitable construction for use in connection with the
apparatus of the invention. Semi-rigid containers and flexible bags
are also included, as are suitable canisters for retaining
fluid.
[0048] In embodiments of the invention where the fluid container is
flexible, it can be deformed while still retaining its function to
contain fluid. The flexible fluid container under negative pressure
suitably does not self-occlude and allows fluid or gas flow from
the wound dressing. The flexible fluid container may be composed of
any suitable material, for example a flexible polymeric film, such
as polyurethane, PVC etc.
[0049] The flexible fluid container will incorporate a means to
allow gas transfer between the internal space of the container and
atmosphere. In embodiments in which fluid is pumped into the
container then an outlet in the form of a vent will be incorporated
to allow trapped air to escape to atmosphere thus preventing the
container becoming pressurised. This vent may consist of a
hydrophobic membrane such as Versapor filter membrane 3 micron
manufactured by Pall Corporation which is bonded in position by
welding or adhesion, the vent function may also be provided by a
conventional pressure relief valve.
[0050] Common practice in the art prior to the present invention is
to use rigid containers that are subject to negative pressures.
[0051] In some embodiments, the fluid container may also comprise a
spacer to manifold the air and fluid. The spacer fabric may be
composed of any suitable fabric. In certain embodiments, the spacer
fabric may be a type of open-cell foam, suitably in the form of a
polymeric material, which can have a honeycomb or multi-chambered
structure.
[0052] In some embodiments of the invention in which the fluid
container is rigid, the microporous fluid separator is suitably
positioned within the canister. In alternative embodiments, where
the fluid container is a flexible container, the microporous fluid
separator may be present as an integral part of the container
rather than a separate part.
[0053] The fluid container according to any embodiment of the
invention may also suitably comprise a fluid absorbing substance
(super-absorbent gel), and/or an odour reducing element (for
example, an active charcoal filter), and/or a deodorising
substance.
[0054] Suitably, the fluid container (11) has an outlet in the form
of a valve or vent to act as a microporous fluid separator which
allows multi-orientation of the container while still allowing gas
flow.
[0055] The fluid container may be present in the form of a cylinder
or a sphere. The fluid container may also have a means of
indicating when it is full. This may be via a visual indicator on
the container itself or an external device which activates when the
pump reaches its maximum capacity.
[0056] In the case of a flexible container the expansion of the
container is constrained by a flexible strap, retaining plate or a
partly rigid housing. This is achieved by the container locating on
a fixed surface such as the product enclosure and the strap or
retaining plate latching in position. As the container fills with
fluid the container is allowed to expand to a pre-determined level
because the constraining means i.e. the strap or retaining plate
has a limited amount of movement or extensibility, When the limit
of the extension is reached the fluid container reacts against the
fixed surface that contains a switch mechanism such as a
micro-switch or a pressure pad and at a pre-determined force this
will be triggered signalling the container is full. In other words,
the expansion of the container may trigger a switch mechanism such
as a micro-switch or a pressure pad by reacting against a flexible
strap, retaining plate or a partly rigid housing.
[0057] An example of a flexible strap arrangement for this purpose
is a strap manufactured from Polypropylene webbing, Code No. W19 as
supplied by Pennine Outdoors. In order to provide some tension to
ensure the strap remains in position during use and also holds the
container securely an elastic fabric strap 10 to 12 mm in width is
stitched or bonded to a section of the webbing strap and pulls the
strap tight in position. This has the effect of providing a limited
amount of extension to the strap arrangement and effectively
pre-tensions the strap.
[0058] Alternatively a strap could be provided that is elastic in
nature but has a pre-determined maximum extended length.
Alternatively the strap may include electrical contacts that make
or break a detection circuit when the expansion of the container
causes the contacts to close or open. To ensure the pump will not
function without the strap or retaining plate in place which
potentially may result in the device not detecting when the
canister is full, a sensor may be incorporated into the strap or
retaining plate mechanism to detect that it is fitted correctly. An
example of a sensor that could be used is a magnetic type proximity
switch such as those produced by Comus International, US. These
devices are triggered by the presence of a magnetic field which
could be provided by a magnet incorporated into the strap or
retaining plate, ideally both states could be detected i.e. in
position and not in position, and this could be achieved by a
changeover type device or through logic within the pump control
system. This information could then be used to prevent the pump
from starting and simultaneously advising the user via an
illuminated LED or audible noise that the strap must be in the
correct position.
[0059] In the case of a rigid fluid container, a means of detecting
when the canister is full can include a capacitive liquid sensor
(examples of which are manufactured by Gill Sensors of the UK and
also Honeywell Sensing and Control of the USA). Other means include
optical sensors and direct pressure transducers. The output of the
chosen sensing means for both flexible and rigid could be used to
send a signal to the pump to switch off, this signal could also be
used to provide a signal to a control panel or an alarm indicator
top alert the user that the canister needs changing.
[0060] The pump can be a peristaltic pump, a diaphragm vacuum pump
or a rotary vane pump. The outlet in the container can be a vent or
valve. The container may contain a means of reducing odour, such as
an activated charcoal filter or a super absorbent gel to solidify
the fluid.
[0061] In the various aspects of the invention, reference is made
to the use of different pumps. As the skilled person in the art
will be aware other suitable sources of a vacuum could also be used
in place of said pumps. Other vacuum sources include but are not
limited to: hospital wall suction devices; portable suction
devices; bellows suction devices and suction devices powered by a
spring means.
[0062] For example, a peristaltic style pump could be used in place
of a traditional air pump. Tubing may be connected from the wound
dressing site and can be fed through the peristaltic pump head,
connecting directly into the fluid container. A microporous fluid
separator (e.g. a hydrophobic filter) can be provided at the outlet
of the fluid container to expel the air drawn through the system.
The vacuum level induced at the wound site can be controlled by the
speed of the peristaltic pump.
[0063] The invention therefore also provides the use of a positive
displacement pump normally intended for pumping fluids and not for
generating negative pressures.
[0064] The mechanical pressure control valve may be a pressure
relief valve. In some embodiments, the mechanical pressure control
valve may be a vacuum control valve. The pressure control valve may
consist of a spring element and a seal element. The pressure
control valve may be orientated with the seal element on the outlet
port to atmosphere. The pressure control valve may be provided as a
"duck-bill" valve.
[0065] Where the pressure control valve is a standard pressure
control valve it can be used in the reverse orientation i.e. the
normal outlet to atmosphere is connected to the fluid side.
Alternatively, the valve can be designed to operate in this fashion
to permit airflow into the dressing.
[0066] The invention therefore provides the use of an air pressure
control valve to act as a check valve when fitted in the reverse
orientation and subjected to fluid pressure on the normal
outlet.
[0067] The invention therefore includes the use of a standard type
pressure control valve originally intended for a pneumatic
application in reverse with the intended outlet port orientated on
the fluid side of the wound dressing. It is envisaged a custom made
vacuum control could also be used.
[0068] The fluid container in either the rigid or flexible
embodiment contains a microporous fluid separator which in this
aspect acts as a vent or valve. The microporous fluid separator may
be a filter. The filter may be coated in order to provide
hydrophobic and/or oleophobic properties. As liquid is drawn off
the wound it collects in the fluid container but does not exit the
container due to the hydrophobic/oleophobic properties of the
filter and the permanent fixture method to the container material
by the use of adhesives or welding.
[0069] The entire system except the pump may be disposable and
composed of suitable materials that will facilitate disposal,
recovery and/or recycling.
[0070] The apparatus therefore provides a closed loop system, in
which the pressure control valve acts to control the system without
further input.
[0071] The various elements of the apparatus such as the wound
dressing, tubing, tubing connectors and fluid container described
above may be sterilised prior to use, or provided in sterile
ready-to-use forms, suitably in air-tight blister-packs.
Sterilisation may be achieved by any suitable means.
[0072] Preferred aspects for the second and subsequent aspects of
the invention are as for the first aspect mutatis mutandis.
[0073] According to a second aspect of the invention there is
provided an apparatus comprising a wound dressing (15) connected in
series to a fluid container (11) which is connected in turn through
a microporous fluid separator (7) to a pump (3), the fluid
container is provided with an inlet and an outlet, wherein the
wound dressing is in communication with a pressure control valve
(13) connected in the reverse orientation.
[0074] In this aspect of the invention, the microporous filter is
present in the line between the pump and the fluid container. In
one embodiment, the microporous fluid separator will be
incorporated into the line between the fluid container and the
peristaltic pump and a one way valve or air bleed is provided at
the end of the tube which vents to atmosphere. Suitably, the fluid
separator may be a hydrophobic filter, typically with a pore size
of 0.45 microns. The advantage of this embodiment is that the
entire tubing set including dressing and fluid container is
isolated from the pump system and therefore any risk of
contamination of the device is eliminated. The pump is therefore
placed at the end of the tube set which draws fluid from the wound
dressing into the fluid container. The fluid container is suitably
a flexible container. The flexible fluid container under negative
pressure suitably does not self-occlude and allows fluid or gas
flow from the wound dressing.
[0075] The invention in accordance with the first and second
aspects of the invention therefore provides the use of a flexible
bag concept to contain fluids which is designed to be subjected to
negative pressures with an integrated bacterial barrier
membrane.
[0076] The fluid container may also comprise a spacer to manifold
the air and fluid. The spacer fabric may be composed of any
suitable fabric. In certain embodiments, the spacer fabric may be a
type of open-cell foam, suitably in the form of a polymeric
material, which can have a honeycomb or multi-chambered
structure.
[0077] In embodiments of the invention in accordance with the first
and second aspects of the invention in which the fluid container is
rigid, the microporous fluid separator is suitably positioned
within the canister. In alternative embodiments, where the fluid
container is a flexible container, the microporous fluid separator
may be present as an integral part of the container rather than a
separate part.
[0078] According to a third aspect of the invention, there is
provided a wound dressing comprising an absorbent pad (for example
a porous pad), a flexible covering (for example a film covering)
and a connection to a mechanical pressure control valve in the
reverse orientation. Such wound dressings are therefore suitable
for use in an apparatus, system or method of the present invention
as described herein.
[0079] According to a fourth aspect of the invention, there is
provided a multi-compartment wound fluid container (20) comprising
at least two internal compartments and provided with an outlet (31)
and an inlet (19), in which the container comprises a microporous
fluid separator (29) which divides the at least two internal
compartments, wherein the microporous fluid separator permits gas
flow between the compartments and prevents fluid flow to the outlet
of the container.
[0080] Such containers suitably comprise two compartments. The
fluid container may be rigid or flexible. The construction of the
fluid container may be as described above in relation to the other
aspects of the invention. The fluid separator suitably acts to
prevent egress of fluid from the outlet of the container.
[0081] In one embodiment, the fluid container (20) comprises a
microporous fluid separator (29) which is positioned to divide the
container wherein the container is provided with a polymeric
material (25, 27) either side of the fluid separator.
[0082] The polymeric material suitably acts as a spacer material in
the container and anchors the fluid separator within the container.
The container suitably comprises film layers (21, 23).
[0083] In another embodiment, the fluid container (35) comprises a
plurality of microporous fluid separators (41) arranged within a
housing (39) provided with a plurality of pores (43) which is
positioned to engage with the outlet (37) of the container wherein
the container further comprises an internal polymeric material (47)
arranged at the inlet (49).
[0084] The microporous fluid separators may be filters, for example
a hydrophobic filter as described herein.
[0085] In an embodiment of this aspect of the invention, the fluid
container may be provided with a supported cylindrical microporous
fluid separator (e.g. a hydrophobic filter). The support for the
separator has an array of holes to allow gas communication with the
separator (e.g. a hydrophobic filter). This allows for the
container to be used on its side and back without disrupting the
function.
[0086] In an alternative embodiment, the fluid container (63) is
rigid or substantially rigid in which the microporous fluid
separator (55) is arranged around a housing (57) internally
disposed within the lumen of the container which is supported by
means of a flexible connector (53) to the outlet (51).
[0087] The purpose of this is to enable the microporous fluid
separator to float on any liquid which may be present in the
container, therefore allowing a gas pathway to be present despite
the orientation of the canister. Only when the container is
completely full with there be no gas communication.
[0088] The microporous fluid separator may be a filter, for example
a hydrophobic filter. The flexible means of support (53) can be a
coiled tube.
[0089] Such containers may be used in conjunction with any aspect
of the invention as defined herein.
[0090] According to a fifth aspect of the invention, there is
provided a system for applying a sub-atmospheric pressure to a
wound dressing on a patient, wherein the system comprises an
apparatus as defined above in accordance with any aspect of the
invention and a control means. The apparatus can be controlled via
a suitable electric circuit which operates the pump.
[0091] According to a sixth aspect of the invention, there is
provided a method of treatment of a wound in a patient comprising
the steps of applying a wound dressing of the present invention to
a wound and connecting the wound dressing to fluid container as
described herein where the wound is kept under negative air
pressure. The negative air pressure can be provided by connecting
the fluid container to a source of a vacuum or a suitable pump.
[0092] Examples of apparatus, systems and fluid containers
according to the invention are described further below and in the
drawings.
[0093] The advantage of the present invention solution is that it
addresses the fundamental problems associated with using NPWT
treatment which was originally developed for the hospital market
for use in the home and community market.
[0094] Specifically: [0095] The present invention provides a means
of delivering NPWT effectively at the wound site in a very simple
form without the need for expensive electronics. [0096] The
accuracy of the pressure control at the wound is very high because
it is directly controlled. [0097] The pressure control means allows
the fluid to be constantly aerated at the wound site allowing the
fluid to be effectively withdrawn from the wound site reducing the
risk of "pooling" and the associated risks i.e. maceration,
infection etc. [0098] The use of this design of valve i.e. a
pressure control valve in reverse provides an effective means of
sealing the dressing against fluid leakage when the negative
pressure is removed. [0099] The means of controlling pressure at
the wound site allows alternative pump type systems to be used such
as Positive Displacement Pumps which include peristaltic pumps.
Previously these could not be used without wound site pressure
control because the sealed nature of these systems means that
pressure at the wound site cannot be controlled by reducing speed
of the pump as is the case with conventional air pumps. [0100] The
direct pressure control allows other vacuum sources to be used that
previously could not be used because they require regulation at
source, this includes wall suction or potentially a mechanical
means such as bellows or sprung loaded vacuum generation device.
Provided the vacuum source is higher than the required wound site
target pressure then the pressure control valve at the dressing
will maintain the correct pressure at the wound. [0101] The
invention allows the use of a flexible fluid container; this
reduces material cost, size and weight. User acceptance is higher
because it is more conformable and the concept of wearing a
flexible fluid container is also accepted in the homecare
environment e.g. urinary and colostomy bags. [0102] The invention
solution can utilise procedures that are already in place for the
disposal of these types of flexible bags thus reducing the
environmental impact over the incineration of a rigid moulded
container. [0103] The invention allows the product to operate
through a range of orientations whilst subject to movement and
vibrations and still adequately fill the container with wound
fluid. [0104] The pressure can be maintained at the wound site
without the complexity of multiple pressure sensors, signal
conditioning circuitry and pressure control algorithms. [0105]
Overall cost, size and weight are reduced. [0106] The direct nature
of the pressure control at the wound site results in a very
efficient use of the vacuum source because the rest of the system
can be air tight resulting in very low noise and very low power
consumption.
[0107] In the application reference is made to a number of drawings
in which:
[0108] FIG. 1a and FIG. 1b show systems of the invention
[0109] FIG. 2 shows a system of the invention
[0110] FIG. 3 shows a flexible fluid container of the
invention.
[0111] FIG. 4 shows a flexible fluid container of the invention
[0112] FIG. 5 shows an alternative embodiment of a flexible
canister of the invention
[0113] FIG. 6 shows an alternative embodiment of a flexible
canister of the invention
[0114] FIG. 7 shows an alternative embodiment of a rigid canister
of the invention
[0115] FIG. 8 shows an isometric view of an embodiment of an
apparatus of the invention
[0116] The invention will now be further described in detail with
reference to the following Figures and Examples which are not to be
construed as being limitations to the invention.
[0117] FIG. 1a and FIG. 1b show systems of the invention whereby a
wound dressing is connected to a fluid container (11) via tubing
(5) which is suitable for use with a peristaltic pump. Connected in
proximity to the wound dressing is a pressure control valve (13)
which limits the negative pressure produced at the wound site to a
predetermined value. The fluid container (11) can either be rigid
or may be flexible to allow conformity to the patient (this is
described in further detail in FIG. 3 below). The container has an
inlet (2) and an outlet (4). Between the container (11) and wound
dressing (15) a peristaltic pump (3) is used. The tubing (5) is
connected through the peristaltic pump. The container has a means
to allow the gas to escape such as a vent or valve (1) positioned
at the outlet (i.e. an air control valve), thereby preventing over
inflation of the container in its flexible form and would typically
incorporate a hydrophobic filter to ensure the fluid is contained.
The container could also contain a means of reducing odour such as
an activated charcoal filter or a superabsorbent gel to solidify
the fluid. An example of a suitable style of container for this
purpose is a 540 ml vented urinary bag such as that manufactured by
Hollister Inc., USA.
[0118] FIG. 1a shows one embodiment of the invention of a system in
which the outlet (4) comprises a vent suitably composed of a gas
permeable hydrophobic membrane as described herein. FIG. 1b shows
an alternative embodiment in which the outlet (4) comprises an air
control valve (1) as described herein.
[0119] FIG. 2 shows a wound dressing (15) connected via tubing to a
container (11) where the wound dressing is provided with a negative
pressure control valve (13). The container (11) is connected to a
hydrophobic filter (7) via tubing (9). The filter is connected to
an air control valve (1) by tubing (5) that is suitable for use
with a peristaltic pump (3). The container (11) can either be rigid
with a hydrophobic filter integrated within, or a flexible
container as described in FIGS. 3 and 4. In the latter two
embodiments, the hydrophobic filter (7) is no longer present
externally since a corresponding filter is present within the
container.
[0120] A pressure control valve (13) as shown in FIGS. 1 and 2 is
positioned in reverse to its normal orientation between the fluid
container (11) and the wound site dressing (15) to provide better
pressure control, due to the closer proximity to the area requiring
regulated pressure and therefore is not prone to the hydrostatic
head effect caused by pulling fluid upwards. Additionally by
placing the pressure control mechanism on the wound side of the
hydrophobic filter then the effect of the pressure drop across the
filter is eliminated. Typically the pressure control valve would be
set at a pre-determined pressure such as 2.5 PSI (129 mmHg) with a
5 to 15% crack tolerance. A standard arrangement for this type of
valve is 3 ports with the control element consisting of a polymeric
seal such a silicone and a stainless steel spring inside a
Polypropylene or similar injection moulded body. An example of this
is available from Qosina Part No. D002501. A large range of
alternative valve arrangements could be used including Duck Bill
style valves orientated in a reverse configuration i.e. with the
valve seal lips on the fluid side. Another alternative is an
Umbrella style control valve. A traditional style ball and spring
valve could also be used. It is envisaged a purpose made vacuum
valve could also be used. Typically a range of dressings will be
available for differing wounds such as leg and pressure ulcers and
the dressings will be matched in size and pressure settings to
accommodate this. Additionally valves will be available that can be
adjusted by the user and may be situated at various positions from
the dressing to the negative pressure source.
[0121] One method of negative pressure generation is by a
peristaltic pump (3) as shown in FIGS. 1 and 2. This pump allows
for a combined, disposable set of components to be used. No fluid
comes into contact with the pump and this omits the requirement for
protective filter systems for the pump. With the use of the
pressure control valve (13) that limits the pressure at the wound
site, the control system for the pump is limited. A potential
peristaltic pump could be the 400F/A Single Channel Precision Pump
by Watson Marlow Alitea. Other types of positive displacement pumps
could be used and integrated into the tubing set such as a
disposable pump head, an example of this type of pump is the
CAPIOX.RTM. Disposable Centrifugal Pump manufactured by Terumo,
USA. Another example of a pump that could be used is a Kamoer KPP
Peristaltic dosing pump that has additional advantages of a small
size and low power requirements.
[0122] An alternative to a peristaltic pump is a small diaphragm
vacuum pump with a flow rate of between 1.5 litres and 2 litres per
min at free flow with a maximum vacuum of 370 mmHg an example of
this would a pump manufactured by KNF Neuberger GmbH of Frieburg,
Germany Model number NMS020L. A range of other vacuum pumps could
be utilised with a range of flow rates up to 10 litres per min if
required. For the community application minimum user controls are
required so normally the device would be pre-set at a vacuum level
slightly above the required wound site pressure level to account
for variances in pressure due to height differences etc. In
practice this will result in a small constant flow of air at the
wound site which will ensure there is mobility of the wound fluid
from the dressing to the container.
[0123] FIGS. 3 and 4 show flexible fluid containers of the
invention. The hydrophobic filter (29) is encapsulated between the
two films (21, 23) that form the container and this effectively
produces a wet side and dry side over the entire area of the
filter. Sections of a spacer material (25, 27) prevent the film
collapsing and occluding the filter and also provide a means of
manifolding the fluid evenly within the container. Because the
filter covers the entire area of the container in any orientation a
section of the filter will be open until the container fills to its
full capacity. The filter surface is treated to ensure it is both
Hydrophobic and Oleophobic and therefore will resist wetting by
either water based liquids or fats and lipids. This means that
splashing of fluids will bead on the surface and not spread over
the surface of the filter. The super absorbent gel also immobilises
the fluids and prevents splashing.
[0124] The fluid container consists of two layers of Polyurethane
film (21, 23) such as that manufactured by Chorino Grade UE80 or
Epurex Platilon Grade U073 manufactured by Bayer. PVC material
could also be used, the material used in the construction of blood
bags is particularly suitable, an example of this type of material
is Renolit Solmed Transufol Seta 3224 manufactured by Renolit,
located in the Netherlands. Within these two layers a hydrophobic
filter (29) such as Versapor filter membrane 0.8 micron
manufactured by Pall Corporation is encapsulated by RF welding,
Ultrasonically welding, heat impulse welding or bonding to the film
layers. Alternative membrane pore sizes could be used ranging from
0.2 micron to 10 micron could be used. Either side of this filter
is sections of a spacer material (25, 27)); an example of this is
manufactured by Mueller textiles of Germany, Grade 5754. Another
example is Stimulite.RTM. manufactured by Supracor.RTM. of USA,
which is a flexible bonded honeycomb polymer which provides
resistance in one plane but allows flexibility in the others.
Additionally other materials may be added such as an active carbon
filter to reduce odour or a super-absorbent gel such as a Sodium
Polyacrylate composition to partially solidify the fluid (this
would be incorporated into 27). Connected to the flexible container
assembly an inlet (19) and outlet (31) tube or port is hermetically
joined by RF welding, UV or solvent bonding or by a similar
process.
[0125] The outlet tube or port is connected to a negative pressure
air source (indicated by air flow direction arrow (33)) that
evacuates the air within the system and at the wound site dressing.
Typically the pressures will vary between 25 mmHg and 200 mmHg.
[0126] The inlet tube (19) is connected to a wound dressing (and
air flow direction arrow (17) shows the flow of liquid from the
wound into the dressing). Various volumes of the flexible container
can be produced according to the required clinical application but
for the homecare application then this typically would be 100 ml.
Utilising this principle, containers with different capacities
could be produced between 50 ml and 5 litres.
[0127] FIG. 5 shows an end section of an alternative flexible
container. FIG. 6 shows a front section of the fluid container (35)
is a flexible sealed container of a PU film which is RF Welded
together. A fluid inlet (49) is bonded into the film. A vacuum
source outlet (37) is fitted into the fluid container at (45).
Within the sealed fluid container is a flexible, non-compressible
material (47) that prevents the fluid container from self-sealing,
thereby preventing fluid to be drawn into the fluid container. The
vacuum source tube (37) fits into a cylindrical plastic component
called the filter housing (39). This has a series of ribs along the
length that prevents the film of the fluid container from adhering
to the hydrophobic filters (41) when subjected to negative
pressure. Holes (43) in the housing (39) allow gas to pass between
the interior of the filter housing and the space around the
housing. The benefit of this design is to allow for a
multidirectional fluid container whereby only until the canister is
completely full will the filter membrane be occluded which will
prevent further fluid uptake.
[0128] FIG. 7 shows a cross sectional front view of a rigid fluid
container (63) with fluid inlet port (59) and outlet port (51). The
outlet port passes through (63) and is fixed at the intersection.
The outlet port (51) is connected to a coiled, flexible tube (53).
This is fixed to a hollow sphere (53) which has a plurality of
holes allowing gas communication between the hollow interior of the
sphere and the fluid container. Surrounding the sphere (57) is a
hydrophobic filter (55) which covers the holes and prevents fluid
passing into the sphere but allows gas to pass from the inlet (59)
through the sphere and through the outlet (51) to a vacuum source.
When fluid (61) is present in the fluid container, the sphere is
allowed to float on the level at any orientation whilst still being
connected via the coiled tubing (53).
[0129] The embodiment as shown in the drawings has been prototyped
and tested on the bench. This proved that pressures could be
maintained within a small tolerance at the wound site utilising a
mechanical valve arrangement over a range of conditions which
simulated real clinical conditions. Additionally it was proved that
a flexible fluid container could be produced with a hydrophobic
filter barrier. The prototype was able to function under 200 mmHg
of negative pressure and uptake fluid into the fluid chamber. No
fluid passed through the filter barrier. The following test results
show the invention in practice.
[0130] FIG. 8 shows an isometric view of an apparatus of the
invention in which a wound dressing (15) is in communication with a
mechanical pressure control valve (13). The wound dressing is
connected via tubing (5) to a fluid container (11) via a pump
(3).
EXAMPLES OF THE INVENTION
[0131] Testing was carried out utilising the arrangement as
described in FIG. 1. The test equipment and components used were as
follows: [0132] Watson Marlow 102U Bench top Peristaltic Pump
[0133] Watson Marlow Peristaltic tubing Pumpsil 913A (4.8 mm
bore.times.1.6 mm Wall) [0134] Test dressing (100 mm.times.50
mm.times.30 mm) 150 cc Volume [0135] Pressure control Valve. Qosina
D002501. 2.5 PSI Cracking pressure+/-15% [0136] Manual Vacuum
Gauge. SM Gauge. 1.6% Accuracy over Full Scale Deflection.
Test 1 (Pump Between Dressing and Fluid Container) See FIG. 1
Test 1a: Closed System, No Pressure Control Valve
TABLE-US-00001 [0137] Pump Fluid Pressure speed flow at dressing
Comment 200 RPM 0 >350 mmHg Closed system 30 RPM 0 >200 mmHg
30 RPM to 200 mmHg Pressure not reduced by reducing 5 RPM pump
speed. System needs to be opened to achieve pressure decay
Test 1b: Pressure Relieve Valve (Inverted) Placed at Dressing
TABLE-US-00002 [0138] Pump Fluid Pressure speed flow at dressing
Comment 30 RPM 0 120-125 mmHg Reached 150 mmHg (cracking pressure)
in 60 seconds stabilised to 120 mmHg 200 RPM 0 120-130 mmHg Valve
compensated for increased flow to maintain constant pressure
Test 1c: Fluid Introduced, Pressure Valve Fitted
Pump Speed Set to Maintain a Constant Fluid Flow
TABLE-US-00003 [0139] Pump Fluid Pressure speed flow at dressing
Comment 30 RPM 12.5 ml/hour 120-125 mmHg 30 rpm maintains constant
flow rate
Test 1d: Height Difference Introduced (Dressing Set at 0.5 Metres
Below the Pump Unit)
TABLE-US-00004 [0140] Fluid Pressure Pump speed flow at dressing
Comment 30 RPM 12.5 ml/hour 120-125 mmHg No pressure drop off due
to height difference
Test 1e: Overnight Test Using Realistic Wound Exudate Flow
Rates
TABLE-US-00005 [0141] Pump Fluid Pressure speed flow at dressing
Comment 5 RPM 2.25 ml/hour 120-125 mmHg Test run for 20 hours, 45
ml fluid removal
Test 2: Inline Container Test. See FIG. 2
TABLE-US-00006 Pump Fluid Pressure speed flow at dressing Comment
62 RPM 210 ml/hour 120 Rapid filling test, 14 minutes to full mmHg
canister (50 ml). Pressure maintained at dressing side
Conclusion of Testing
[0142] Test 1a). With a closed system (air only) utilising a
peristaltic pump it was demonstrated that the pressure could not be
controlled adequately, as the pump speed increased the pressure
correspondingly increased to in excess of 350 mmHg. Decreasing the
pump speed did not effectively reduce the pressure and it remained
at over 200 mmHg even at the lowest setting used of 5 RPM. Any
pressure decrease was only due to connector leakages and the
breathability of the drape.
[0143] 1b). With the pressure valve fitted at the dressing site at
full speed of 200 mmHg the wound site pressure was limited to 120
mmHg+/-2.5 mmHg with a momentary maximum of 150 mmHg as the valve
initially opened.
[0144] 1c). With fluid introduced at 30 rpm a constant flow rate
was achieved. The fluid flow was aided by small amounts of air
being drawn through the valve which allowed mobility of the fluid
from the dressing to the container.
[0145] 1d). Changing the height of the dressing relative to the
pump (0.5 metres) did not result in any measurable pressure change
at the website.
[0146] 1e). A longer duration test (20 hrs) showed over an extended
period a low level of fluid (2.25 ml per hour) was withdrawn at a
constant rate without any issues or alterations in parameters, the
flow rate was set at a very low flow rate (5 rpm) which results in
very low noise levels and power consumption. This flow rate is
equable to certain types of leg and foot ulcers.
[0147] Test 2). The inline container configuration was tested at a
relative high flow rate 210 ml/hour to stress the filter. The
container filled to capacity, maintained the target pressure and
the filter was not breached.
Results of the Testing:
[0148] A standard pressure control valve was used in the reverse
orientation i.e. the normal outlet to atmosphere was connected to
the fluid side, the variance of negative pressure readings was well
within the stated manufacturers tolerance of +/-15%, which would
normally relate to a total tolerance of 38 mmHg at the normal
working pressure. The pressures measured after the valve originally
opened and the pressure stabilised to be in the order of 10 mmHg
total working tolerance.
[0149] This is believed to be significantly more accurate than
electronic control systems that rely on multiple conduit pathways
and multiple electronic components.
[0150] The introduction of the pressure valve had a second effect
beyond pressure control that was not anticipated, this was to allow
the introduction of small amounts of air into the system at the
dressing site. This had two effects, the first was to allow
constant flow of fluid from the dressing at a very low flow rates,
the second was to provide a mechanism to reduce pressure at the
wound site when sealed pump systems such as a peristaltic pump is
used. Additionally the valve had the effect of aerating the fluid
evenly causing mobility which appeared to be different in nature
when a basic leak is introduced through an orifice. One explanation
for this may be due to the design of the valve and the
characteristics of the sprung loaded component and seat, although
this valve is designed to relieve positive air pressure it has an
advantageous effect in regulating air inflow under negative
pressure when fitted in reverse. A second major advantage of the
valve arrangement is due to the reverse nature of the sprung loaded
action when fluid is forced back into the dressing the valve will
be forced closed effectively sealing the dressing. Several
scenarios exist when this can happen; one example is when therapy
is paused for when the patient is taken a shower, in this case
gravity or pressure against the dressing could cause fluid to pool
in the dressing. Normally if the dressing contained any passage to
atmosphere then fluid could leak out causing an infection risk.
[0151] In the case of devices that contain sensing tubes or
conduits to the control unit to control pressure these can
potentially fill with fluid when negative pressure is paused that
may cause blockages, this situation is eliminated in the present
invention.
* * * * *